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Introduction to Matlab
T.E. Ochsner2011
Getting Started with Matlab
• http://www.mathworks.com/videos/matlab/getting-started-with-matlab.html
OSU Matlab Site License
• E-mail Gary Hoefar in the IT Dep. [email protected]
• Request access to download and activate Matlab.• After you get Gary’s response, go to
http://www.mathworks.com/• Create an account using the same name and e-mail
you gave Gary.• Download, install, and activate the appropriate
version for your operating system– Current release is R2011a
Weak traceability
Record data in field or lab book
Enter data in Excel
Perform some calculations
Enter some parameters in Excel
Copy and paste the tranformed data into a convenient
format for SAS
Import the transformed data to
SAS and do some more calculations
Enter the SAS output into a table
in your thesis
Import the transformed data
into SigmaPlot
Create some figures in SigmaPlot
Copy and paste the SigmaPlot figures in
your thesis
Improved traceability
Record data in field or lab book
Create raw data file in .csv, .xlsx, or other format
Create Matlab script to process
the data, generate figs, and run stats.
Copy and paste the Matlab figures and
stats into your thesis.
Weak graphics
1 1.5 2 2.5 3 3.5 40
5
10
15
20
25
Late Harvest Rye Early Harvest Rye Control
Visual Score
Dept
h (c
m)
Improved graphics
25
50
75
100
2006-2007
Mono cropDouble crop
25
50
75
100
2007-2008 GC
(%
)
2-Sept 3-Nov 4-Jan 7-Mar 8-May 9-July0
25
50
75
100
2008-2009
Customization
function theta_vg = vangenuchten(vgparams, matric)%VANGENUCHTEN returns the estimated water content vector corresponding to%the input vectors containing the matric potential and the function%parameters. The units of the matric potential and the units of the%parameter "alpha" must cancel.
theta_s = vgparams(1); %saturated water contenttheta_r = vgparams(2); %residual water contentn = vgparams(3); %shape factoralpha = vgparams(4); % inverse of air entry potential%m = 1 - 1/n;m = vgparams(5);
theta_vg = ((1+(-alpha*matric).^n).^(-m))*(theta_s - theta_r) + theta_r;
Efficiency and Speed• Excel spreadsheet with 106 data points = 8.8 Mb• Matlab data file with 106 data points = 0.4 Mb• “Consider the problem of inverting the covariance matrix of a first-
order autoregressive process with dimension n=1000 and correlation parameter 0.5 and unit innovation variance…. PC with a 400 MHz Pentium II processor running WinNT with 256 MB RAM.”
Program CPU Time in Seconds
Mathematica, uncompiled 127
Mathematica, compiled 99
R 77
MatLab V.5.3 R11 48
S-Plus Version 5.2 109
C++ 98
Fortran 79
http://www.stats.uwo.ca/faculty/aim/epubs/MatrixInverseTiming/default.htm
Disadvantages of Matlab
• Harder to learn than Excel
• Weaker on statistics than SAS– For example: no built-in “repeated measures”
procedure
